Adjustable wire-wound systems



June 23, 1959 R. E. SEMPLE ADJUSTABLE WIRE-WOUND SYSTEMS Filed March 26, 1956 IN VEN TOR. ROBERT E. SEMPLE A Tr R/vEYs United States Patent ADJUSTABLE WIRE-WOUND SYSTEMS Robert E. Semple, Temple City, Calif., assignor, by mesne assignments, to Con-Elco, a corporation of California iApplication March 26, 1956, Serial No. 573,817

5 Claims. (Cl. 338-180) This invention is directed to improvements in adjustable wire-wound and equivalent systems. I

In the design and construction of potentiometers and other types of wire-wound systems it is frequently desirable to achieve a maximum amount of overall resistance in a minimum volume without sacrifice of required ruggedness, performance characteristics, and economy. The present invention involves a structural principle by means of which this objective may be achieved to a greater extent than has heretofore been attained.

- The structure is unique in the use of a resistance coil core as a skeleton in which the moving parts of the system are enclosed. More specifically the coil is wound on a tubular core which is provided with a longitudinal slot in its wall through which a contactor is caused to contact the inner circumference of the coil Within the linear confines of the core slot. To further effect a conservation of volume, the contactor is mounted on a shaft extending into the core and generally concentrically therein, and preferably the shaft itself is utilized as an electrical lead in the system. In this manner the separate shorting bar conventionally employed in potentiometers is eliminated as a separate structural element.

-In a preferred embodiment of the invention a reinforcing backer is applied over the exterior portion of the coil and of such longitudinal and circumferential extent as to overlie the slot in the core. This backer reinforces the coil in the region of contact engagement and may serve the additional function of an electrical lead from one end of the coil.

i The structure of the invention is particularly suited to embodiment as a so-called miniature potentiometer. Although there is no definition of what is meant by miniature in this field, it is probably accurate to consider any potentiometer of less than about two inches in length and about inch in diameter and having an acceptable resistance range, as a miniature potentiometer. The structure herein described permits the fabrication of a sturdy reliable unit as small as one inch in length and i or even A; inch in diameter and with a widerange of coil resistance such as from about 3 ohms to about 80,000 ohms.

A specific use to which the structure of the invention is well adapted is as a balancing or trimming potentiometer in which the contact adjustment is carefully and minutely made, and is generally left at a circuit balancing value. For this purpose the longitudinally extending contact-carrying shaft is preferably threaded and is journaled through an end of the potentiometer case. Means are provided for externally rotating the shaft to cause accurate adjustment of the contact which, in such embodiment, is threaded on the shaft and held against rotation. Alternatively the shaft can be mounted for linear motion in the direction of the longitudinal axis of the core.

A further feature of the invention is the ease with which the resistor structure can be hermetically sealed.

Conveniently, as above indicated, an enclosing, case. isv

supported about the resistance coil, one end of the case being sealed with a suitable closure through which electrical leads may be carried. The shaft is embedded at one end in an insulating head which in turn is journaled through the end of the case opposite the sealing closure. When a threaded shaft is incorporated, this head is generally spring-loaded against an internal shoulder of the ferred form of potentiometer in accordance with the invention;

Fig. 2 is an end view taken on the line 2-2 of Fig. 1; Fig. 3 is a vertical section taken on the line 33 of Fig. 1; and

i Fig. 4 is an enlarged view of the section 44 of Fig. 3.

The potentiometer comprises a tubular housing 10 including a relatively large section 11A and a reduced diameter end section 11B, which end section is conveniently threaded exteriorly for mounting purposes. A sloping annular shoulder 11C separates the housing sections 11A and 11B internally. A tubular core 12, preferably fabricated of an insulating material such as a Bakelite plastic, has end sections 12A, 12B of a diameter substantially equal to the inside diameter of the case so as- I to fit snugly therein, and a reduced diameter central section 120. The end sections 12A and 12B are also of larger inside diameter than the central section 120.

A longitudinally extending slot 14 is formed in the wall of the central section 12C of the core and a small diameter resistance wire is wrapped as a continuous helical coil 15 about this section of the core enclosing a major portion of the slot 14. The wire is conveniently enamel-coated, with the insulating enamel being subsequently removed from that portion exposed to the interior of the core through the slot 14. Alternatively, bare wire may be used in the formation of a space-wound coil.

A threaded shaft 16 is molded or otherwise mounted into a cylindrical insulating head 17, a major portion of which conforms to the inside diameter of section 11B of the case and is journaled therethrough as indicated. The inner end of the head 17 includes a relatively larger diameter section 17A conforming to the inside diameter of the end section 12B of the core. A coil spring 18 is supported around the head 17 between the enlarged section 17A and the shoulder 11C in the housing. If the system is to be hermetically sealed, the shoulder 110 is preferably inclined as shown, and a sealing 0 ring 20 is mounted on the head 17 and, under the influence of i spring 18, wedged into the annular notch formed by the inner section of the shoulder 11C and the wall of thehead 17. The outer end of the head 17 is provided with a screwdriver receiving notch 21 by means of which the shaft 16 may be rotated. The shaft may be extended outwardly of the case to enable rotation thereof by other a conductive disk, preferably silver, and is embedded in the inner end of a bore 25 in the plug by a suitable plotting material 26. The bearing disk is center-bored to receive cable 27. The cable insulation 28 is preferably carried through the disk bore and the stripped cable wire 29 is soldered to the disk face as shown. This construction serves as a very effective cable clamp as well as a bearing and to provide electrical continuity.

A contact 30 is supportedon a sleeve 31 threaded on the shaft 16 and carrying a boss 32 to which the contract 30 is afiixed. A unique aspect of this contact is that a single metallic strip constitutes an integral contact and spring construction, and the hinge point is actually at a fulcrum remote from the mechanical attachment. In the drawing this hinge point and fulcrum is at 33, whereas the mechanical attachment is at the boss 32. By reason of this remote attachment, any softening of the metal at the hinge point due to welding is eliminated, and the fulcrum is merely a point of contact and not an attachment point.

By reason of the projection of the boss 32 into the slot 14, the sleeve is prevented from rotation and any rotation of the shaft 16 causes a linear displacement of the sleeve along the shaft and hence of the contact along the coil.

A backer strip 36 is cemented to the coil overlying the slot 14, this strip serving to reinforce the coil along the line of contact engagement and also doubling as an inboard lead from the coil. One end of the coil is connected by connector 37 to a conductive portion of the hacker strip which, at its opposite end, is connected to a lead 38 extending through the plug 23. Similarly the inner end of the coil is likewise electrically connected through the plug by a lead 39. The backer may be of either insulating material, and provided with a printed or superimposed conductor along its exposed surface, or the backer itself may be of conductive material suitably insulated from the coil by the coil enamel or by the adhesive by means of which it is applied.

Preferably the inner face of the backer strip is slightly convex, as is particularly apparent in the enlarged section of Fig. 4. This configuration depresses the coil, thereby reducing the contact surface exposed to contactor 30 to essentially a tangential point, resulting in a cleaner contact less susceptible to irregularities in the system. At the same time the distortion of the coil consequent upon this configuration produces a desirable post winding tension serving to equalize the several turns and remove any unwanted slack. The backer strip may be adhered to the coil under pressure so that the deformation of the coil is fixed and retained even after the pressure is removed.

Electrical continuity is established from the contactor through the sleeve, screw shaft, and bearing button to the exterior .of the instrument. This obviates the space requirements of the conventionally separate shorting bus. If a linear displaceable shaft is employed, electrical con tinuity can be established between the contact and a suitable terminal in the plug by interconnection with a helical continuity spring,

If the case is metallic, as is frequently required, it is desirable to interpose an insulating skin between the coil and the case. In the illustrated potentiometer a polytetrafiuorethylene sheet 42 is slipped into the case lying snugly as a skin against the inside wall thereof. Such insulation isolates the coil from the case, preventing electrical leakage which otherwise occurs under certain. circumstances.

The operation of the illustrated Wire-bound resistance system as a potentiometer is apparent. Electrical leads 38 and .39 are connected to opposite ends of the resistance coil and electrical lead 28 through the shaft 16,. and the contact 30 is adjustably connected to tap off a predetermined portion of any voltage applied across the resistor. The instrument may be used in any manus: in which conventional rectilinear otentiometers find use but, as mentioned above, is particularly suited for miniaturization because of its unique and space-saving structure. Although use of the resistance system as a potentiometer has been described and illustrated, it is apparent that the instrument can be employed as an adjustable resistor and as a rheostat.

-An instrument of the type illustrated and described may have the following dimensions and characteristics by way of example:

inch 0D.

1% inch outside length.

Resistance wire from .005 inch to .0006 inch in. diameter. Coil resistance from 3 ohms to 80,000 ohms.

/8 inch electrical travel.

.650 inch active coil length.

As mentioned, these are exemplary values only and are not intended in any way to indicate the limit of miniaturization or enlargement.

The invention has been principally described and illustrated inconnection with a wire-wound system. The structure, however, is also adapted to accommodate other types of resistors; For example, a resistance coating plated, printed or otherwise applied to the inner face .of the backer strip can. replace the wire coil without altering the basic functions of the unit. The application and claims, in referring to wire-wound systems, therefore contemplate embodiment of such other forms of resistance elements in the described structure.

I claim:

1. An adjustable wire-wound system comprising a tubular core having a longitudinally extending slot in its tubular wall, a resistance wire wound as a coil about the core and enclosing at least a portion of the slot, a.

reinforcing backer strip mounted on the exterior of the coil overlying the slot in the core and having a convex inner face bearing against the coil and producing a reverse curvature in the coil in the region of the slot, a shaft supported longitudinally within the core, a contact supported on the shaft and extending through the slot in engagement with that portion of the inner surface of the wire coil exposed by the slot, means operable to displace the contact along the slot, and means for making electrical connections to the coil and the contact.

2. An adjustable wire-wound system comprising a tubalar core having a longitudinally extending slot in its tubular wall, a resistance wire wound as a coil around the core and substantially enclosing the slot, a case enclosing the core and having an opening at one end of smaller diameter than the diameter of the adjacent portion of the core, a plug. enclosing the opposite end of the case, a threaded metallic shaft having an insulating head at one end journaled through the end opening in the case, the shaft extending concentrically through the central section of the core and being rotatably supported at its. other end, a sealing ring disposed around the insulating" head, spring means confined between the sealing ring and a shoulder formed on the insulating head inwardly.

substantially from end to end of the central section, a

resistance wire wound as a coil around the central section of the core and substantially enclosing the slot, a case enclosing the core and having .an opening at one end of smaller diameter than the inside diameter of the adjacent section of the core, a plug enclosing the opposite end of the case and extending into the adjacent. end

section of the core, a threaded metallic shaft having an through the central section of the core and being rotatably supported at its other end in the plug, spring means confined between the inside end wall of the case and a shoulder formed on said insulating head inwardly of the end opening of the case, a sleeve threaded on the shaft, a contact extending from the sleeve through the core slot to engage on the coil, and by abutment on the edges of the slot prevent rotation of the coil, an electrical lead connected to the shaft and extending through the plug, and an additional pair of electrical leads extending from the ends of the coil through the plug.

4. An adjustable wire wound system comprising a tubular core having opposing end sections of the same diameter and an intermediate central section of smaller diameter and having a longitudinally extending slot extending substantially from end to end of the central section, a resistance wire wound as a coil around the central section of the core and substantially enclosing the slot, a case enclosing the core and having an opening at one end of smaller diameter than the inside diameter of the adjacent section of the core and connected to the larger portion of the case by an annular sloping shoulder, a plug enclosing the opposite end of the case and extending into the adjacent end section of the core, a threaded metallic shaft having an insulating head at one end journaled through the reduced diameter end section of the case, the shaft extending concentrically through the central section of the core and being rotatably supported at its other end in the plug, a sealing ring disposed around the insulating head and bearing against the sloping shoulder of the case, spring means confined between the sealing ring and a shoulder formed on the insulating head inwardly of the end opening of the case, a sleeve threaded on the shaft, a contact extending from the sleeve through the core slot to engage on the coil, and by abutment on the edges of the slot prevent rotation of the coil, an electrical lead connected to the shaft and extending through the plug, and an additional pair of electrical leads extending from the ends of the cell through the plug.

5. An adjustable wire-wound system comprising a tubular core having a longitudinally extending slot in its tubular wall, a resistance wire wound as a coil about the core and enclosing at least a portion of the slot, a backer strip mounted on the portion of the coil overlying the slot in the tubular core and depressing the curvature of said portion inwardly in the direction of the slot, a shaft supported longitudinally within the core, a contact supported on the shaft and extending through the slot in engagement with the inner surface of the portion of the coil overlying the slot, means operable to displace the contact along the slot, and means for making electrical connections to the coil and contact.

References Cited in the file of this patent UNITED STATES PATENTS 966,555 Jesse Aug. 9, 1910 1,371,049 Oler Mar. 8, 1921 2,707,811 Projector May 10, 1955 

